The present invention relates to a coated refractory composition for making high quality preforms comprising a refractory material selected from a metal refractory carbide, metal refractory nitride, metal refractory boride or diamond having a coating layer of hydrous alumina, and, more particularly, to a method for enhancing the dispersibility and for improving the oxidation resistance and chemical inertness of such compositions.
U S. Pat. No. 4,249,913 describes a silicon carbide abrasive particle which is coated with alumina to inhibit dissolution in a bonding metal matrix during high temperature processing. The alumina coating, described as a dense, anhydrous and amorphous coating, is applied by sputtering or vapor deposition processes.
U.S. Pat. No. 4,801,510 relates to a composite article comprising 5 to 30 vol % silicon carbide whiskers and 70 to 95 vol % alumina, the articles having a thin coating of alumina. The silicon carbide and alumina in the composite are mixed together by ball milling, hot pressed to form a dense article, then coated with a thin layer of alumina using vapor deposition techniques.